Worldwide demand for vehicles that perform under greater fuel economy and produce fewer environmental pollutants has spurred the automotive industry to research and produce vehicles with alternative power-train architectures, including the hybrid-electric vehicle (HEV). Most HEV power-trains have two separate modes of producing torque and power, a conventional internal combustion engine and an electric motor powered by some type of electrical energy storage unit, such as a battery. Generally, the HEV has been successful in delivering greater fuel economy and lowered emissions than conventional internal combustion engines by utilizing a downsized internal combustion engine and augmenting the engine torque through the electric motor when necessary.
Among the disadvantages of known power-train architectures for HEVs are relatively low performance values in torque, horsepower and acceleration. In order to overcome these disadvantages, particularly in large vehicles that are subject to more demanding duty cycles such as towing, it is known that a sizeable electric motor, typically 25 kW or greater, and comparably large energy storage units could be utilized to meet higher torque and power demands. However, the weight penalty for these larger electric motors and energy storage units would largely offset the benefits typically associated with the HEV, including increased fuel economy and lowered emissions.
In the area of alternative HEV power-train architectures, there continues to be a need for a control strategy that allows the power-train to generate increased torque and power while still providing lowered emissions and increased fuel economy.